We still have the original Serta... horzontal springs mattress that came with our 2003 Lance 1161 truck camper. We have had a topper for many years.
We have slept in our camper 1081 nights.
Recently we decided to upgrade:
There is absolutely no way I could sleep on Memory Foam... it is smothering hot... and want support.
We looked at Serta firm Queen Mattresses... nice... and very heavy.
Way to heavy for an RV... (note each additional 100 pounds translates into a 1% fuel economy loss) and it would prevent the area under it from dispersing condensation from humidity.
We ended up spending $114 for
Extra Plush Bamboo Fitted Mattress Topper that was shipped to our house in 4 days free of charge.
It is so nice we have bought one for our King size bed at home... it is plush, cool, and very supportive. In the winter it insulates you from any cold...
I can't say what works for you... you might read the reviews on the link above. We had trouble cjoosing between this one and the one that the same company makes for the Marriott Hotels.
Good luck... go slow... bedding is a big investment and as others have pointed out... they won't take your bad choices back.
Sleepy